1. Field of the Invention
This invention pertains to cardiac monitoring systems. In particular, this invention relates to ambulatory cardiac monitoring systems where a patient is monitored for a predetermined interval. More in particular, this invention relates to an ambulatory cardiac monitoring system where the patient carries a recorder system and the recorder system is coupled to the patient for continuous monitoring of ECG signals.
Still further, this invention relates to an ambulatory cardiac monitoring system where abnormal ECG signals are recorded on a mini-cassette carried within the recorder system. Further, this invention relates to an ambulatory cardiac monitoring system where the cassette is removed from the recording system after the predetermined time interval and inserted into a scanner system remote from the patient for production of both a trend report and an ECG strip for diagnostic purposes.
More in particular, this invention pertains to an ambulatory cardiac monitoring system where the recorder carried by the patient includes both an analog pre-processor and a first microcomputer which is coupled in feedback relation to the analog pre-processor. Still further, this invention relates to an ambulatory cardiac monitoring system having a recorder system which delays the ECG signal passing from the patient in order to provide a time frame interval within which a particular ECG signal may be analyzed and determinations made of various heart arrhythmias and abnormal events based on a particular patient's ECG signal output.
2. Prior Art
Systems for monitoring and analyzing ECG signals are well-known in the art. In general, there are four types of cardiograms being utilized, i.e., resting cardiograms, stress cardiograms, echo cardiograms, and ambulatory cardiograms. Resting cardiograms systems generally take a sample of an ECG signal over a short period of time in a non-ambulatory environment. Thus, heart arrhythmias which may be chronic or transient, are only displayed in the resting cardiograms when they are chronic. If the heart arrhythmias are transient, there is a low probability that resting cardiogram systems will describe such due to the short time interval period within which they are taken.
Ambulatory electro-cardiogram systems to monitor both the chronic and transient heart arrhythmias are carried by the patient during the performance of his or her activities throughout a predetermined time interval. In some prior art ambulatory electrocardiogram systems, the patient's heartbeat signals are recorded continuously for a predetermined time interval on a portable tape recorder carried by the patient. Subsequent to the recording time interval, a scanning device is used that plays back the tape at an accelerated speed. A technically trained operator monitors an oscilloscope and a tone produced by the scanner to observe and/or monitor any heart arrhythmias. In such prior systems the analysis is highly subjective dependent on the skill of the operator.
Additionally, in such prior art systems, the continuous monitoring of the heartbeat of the patient produces a stream of unwanted data and utilizes expensive scanner system equipment in cooperation with highly skilled technicians for diagnosis of the ECG. Some such prior art systems do not analyze the heart arrhythmias to the quantitative extent of the subject ambulatory cardiac monitoring system, which thus results in some arrhythmias going unnoticed with possible deleterious results.
Ambulatory monitoring devices are generally divided into two categories, the first category being Holter monitoring and the second category being commonly referred to as Event recording. In prior art Holter monitoring devices, the patient is monitored continuously for a predetermined time interval with the subsequent disadvantages as has been previously described.
In Event recording, the system is carried by the patient and includes systems for arrhythmia detection and such is condensed to provide salient events of the arrhythmia. In some prior Event recording systems, chronological logs are not provided to permit a quantitating capability, as is provided in the subject system. In other prior art Event recorders, detected arrhythmias are recorded once each predetermined time interval so that when the system records a specific arrhythmia, the system does not analyze any further incidents of the specific arrhythmia for the predetermined time interval and such is incapable of quantifying data. Thus, in some prior art systems of this type, important arrhythmia data is lost to the diagnostician.
Other prior art Event recording systems do not normalize output signals as a function of a particular patient being monitored. Thus, in such prior art Event recording systems, unwanted data may be taken into account based on a false signal that an arrhythmia has occurred when in fact, that signal is normal when related to that particular patient being monitored.